Status of the TPG

Status of the TPG

E.RadicioniMICE coll. Meeting - RAL, 27-29 Oct.

2004

27/10/2004 E.Radicioni 2

Outline

• Recall of the main characteristics• Construction and operation• First of the detector behavior• Design aspects

– Electronics– Field-cage– Gas– Background


• The TPG is a cylindrical TPC equipped with GEM amplification and a special high-resolution pad-plane

• TPCs with GEMs are actively studied by several groups around the world in view of the linear collider experiments.

• The novelty of the TPG consists in the pad-plane, where projective readout promises high granularity with a reduced number of channels

• Dedicated design choices for MICE were – the dimensions (100cm length, 30cm diameter) to fit

into the tracker magnet– The gas (He) chosen because of its low conversion

probability


Construction

E

B

drift volume

field cage

GEM stage solenoid

read-out plane


The GEM foil• Triple-layer structure• Each layer divided in

8 regions, independently powered

• Max amplification depends on gas and HV. With good gas it can be as high as 106.\


The hexaboard

– ~710000 hexagonal pads

• size: 300 m • pitch: 500 m

– grouped into strips along 3 coordinates at 120 degrees (u, v, w) running at different depths


Strips and pads


300 m

500 m


Spot the error … and correct it!


Hexaboard quality, from this:Layer N

for shorcut: C==0

-20

0

20

40

60

80

100

120

140

0 100 200 300 400 500 600

strip number

C [

pF

]

n:n+1

connector


… to this:


Support structures

1

2 34

5

1. outer metal ring

2. o-rings for gas tightness

3. stiffener plate4. GEMs support

rings5. guard ring



Assembling the detector




The dream team at work


Last computations and timing checks …


... what is this detector trying to tell us ???


55Fe source calibration

• Absolute energy, equalization• Preamp gain calibration is not included

yet• First indications are

– Despite the lack of gain equalization, the energy resolution is already quite good

– The plots are very sensitive to the cuts on cluster size, as expected from a properly working detector


55Fe source

• “beam profile”• Unconnected strips• Ill electronic

channels– Dead– Noisy


• Capability of seeing detector structures

• 55Fe source illuminates the center of the pad plane

• Large lines: spacer grid in between the GEMs: 2mm large

• Thin lines: non-working electronics channels


55Fe source

All clusters

≥2 strips

≥3 strips


U,V vs. W correlations• out-of-line events are

due to lack of gain calibration

• Correlation is important: it can be exploited as an additional tool for getting rid of fake combinations– In addition to the use of

the 3rd projection

• Compass is able to reject (almost all) fakes by this technique

TPG

COMPASS


Low energy tracks

• 500 samples @10MHz

• Ar/CO2 90/10, 10cm/s total 50cm drift path

• e- from Sr source• B=0.07T (1/10

nominal)• Color code gives

charge amplitude


• 2 MeV/c electron in B=0.07T

• Transverse diffusion spreads the charge


Intrinsic resolution• 55Fe X-ray conversion

position can be determined by 2 projections, then cross-checked with the 3rd one.

• The intrinsic resolution is VERY promising

• This has been obtained with a 3cm drift cell.

• Actual resolution over longer drift depends on gas properties.

~40µm

U+V vs. W resolution


Design improvements

• Electronics• Ingredients for good resolution• Gas choice• Discussion on overall parameters• A compact emittometer, alias TPG ?


Electronics

• New electronics from ALICE• Higher integration• Total (including DAQ) 10 CHF / channel• Digitization is close to detector (less

noise)• Data get out from the detector on a few

optical fibers (elegant, simple)• Large range of possible sampling

frequencies up to 40 MHz.

3027 February 2004 Luciano Musa / CERN - PH

ALTRO EVOLUTION

4cards16 ch

13

5 m

m

1998

CHANNELS / CHIP: 1

POWER / CH: 120mW

PRICE / CH: 50CHF

Integrated ADCs2

0 m

m

4 PQFP 100

8 SSOP 28

24 mm

1999

CHANNELS / CHIP: 4

POWER / CH: 80mW

PRICE / CH: 8CHF

2001

CHANNELS / CHIP: 1

POWER / CH: 16mW

PRICE / CH: 5CHF

3127 February 2004 Luciano Musa / CERN - PH

Digital Conditioning of the TPC Signal

EV 1 EV 2

EV 3

EV 1 EV 2

EV 3

EV 1 EV 2EV 3

EV 1 EV 2

EV 3

ADC BC I

TCF BC II


Momentum resolution• Position resolution is driven by

– Readout pitch (fixed)– Diffusion in gas– Ionization and gain

• Gas choice is a key point: we should look for larger gain and ionization and smaller diffusions.

• Momentum resolution is driven by– Position resolution– Number of available points

• From the simple Glukstern formula: 50 points give dp/p resolution factor only 1.5 better than 20 points.

• If more distant points are affected by more diffusion, we should really consider limiting the number of points and the drift length.


Gas choice


Shorter field-cage?He/CO2 1m Ne/CO2 18cm

E 500 V 300 V

Max HV 50 KV 5.4 KV

Drift time 60 s 6 s

Drift velocity 1.68 cm/m 3 cm/m

Sampling freq 2MHz 10MHz

Number of samples 118 60

Trans/long diffusion 1000/1600 m 80/200 m

Specific ionization 10 e-/cm 20 e-/cm

Usable long. Slices 118 20 (shaper limited)

N. Radiation lenghts 6.6 E-4 5 E-4

X-ray abs. Coeff. 2.5 E-5 cm-1 1.2 E-4 cm-1

X-ray abs. probability 1 0.4

Electronics HARP ALICE


Tracks and Background in the short TPG

• Intrinsic occupancy limit of the detector: N.strips/cluster size ~ 200– By exploiting correlations (a-la-compass) one could

maybe do better

• 1 muon per s 6 tracks in one “image”• Number of background tracks (normalized per

MHz imput photons) ~ 0.013 MHz-1

• Quoting Rikard’s computations: 22MHz of photons entering the tracker volume in the upstream spectrometer if this rate is OK there will not be any trouble.

• Photon conversion in the HV membrane could account to the same number as conversions in gas not much of a difference.


Conclusions• The TPG detector is operational in the HARP test-

bed• Placed an order for 2000 channels of the new

electronics• First results indicate performances at the

expected level or better• Several design parameters can be reviewed

– Better gas choice better resolution– Shorter detector less material, straightforward

construction, compact, could stay in shorter solenoid.– Faster drift time less X-ray background– Better resolution

• More results from beam tests in the near future

Documents

Status of the TPG